Assessment of long-term trends for management of Candlewood Lake, Connecticut, USA

Candlewood Lake, the largest;lake in Connecticut, is a pumped-storage reservoir formed in the 1920s for hydropower generation. Since its inception, the lake has experienced shifts in water quality coupled with watershed development and, in the 1980s, the introduction and spread of the invasive macrophyte, Myriophyllum spicatum. In response, a monitoring program to track water quality, and a winter drawdown program to mitigate growth of M. spicatum were initiated in 1985. Recently it was sugpested that the drawdovvn program exacerbated eutrophication of the lake. To test this hypothesis, statistical analyses of the long-term (1985 to 2012) database was conducted with a focus on trophicrelated variables. We examined the database using principal component analysis (PCA) and multivarite singular spectrum analysis (MSSA). MSSA is an extension of PCA for multivariate time series data that accounts for both temporal and cross-sectional dependencies We found no evidence that the trophic condition declined, or that the drawdowns have deteriorated the water quality. Instead, we found that lower TS, TSIchi, and TSSD values corresponding with improved trophic conditions occurred in summers following deep drawdowns, while significantly higher values correlated with shallow and less effective drawdowns. Overall, there has been a modest improvement in the trophic condition overtime, attributed to a combination of the winter drawdowns and management efforts. In contrast, a steady and significant increase in dissolved salts, likely due to enhanced use of road deicing treatments, was documented.